1. Field of the Invention
The present invention relates to digital data distribution technology, such as digital satellite broadcasts and multimedia content communication, and in particular, relates to a technology for distributing digital data composed of computer language instructions having data attributes. Digital data composed of instructions of a computer language having data attributes is described, for example, by a markup language format composed of tag data delimited by tags which define data attributes.
More particularly, the present invention relates to a technology for distributing digital data in a markup language (for example, XML (eXtensible Markup Language)) format in which tags which can be defined arbitrarily are used and in particular, relates to handling of style sheets (for example, XSL (eXtensible Stylesheet Language)) documents for defining the expression form, etc., of distribution data composed of XML documents, etc.
2. Description of the Related Art
In the technical field of satellite television broadcasts, digitization of data is progressing rapidly. This is because use of digital data allows a broadcast band to be used more efficiently than does use of analog data and digital data has a greater compatibility with data other than video and audio data.
For example, in the case of digital data, it is possible to carry data for four data streams in one channel, and data for high-definition television can be transmitted as it is. Also, by sending various types of system information, such as an EPG (Electronic Program Guide) together with video information and audio information, services for users (viewers) can be improved.
Data in digital form is highly compatible with general-purpose computer systems. For example, by mounting a satellite tuner card in a general-purpose computer system, by analyzing received EPG data in a computer, and by window-displaying a program menu on a computer display, program changes and recording program settings can be realized by an operation using a mouse and cursor keys. Of course, broadcast data can also be digitally recorded as it is in a hard disk contained in a computer.
Also, by transmitting data other than that for video, it is possible to increase interactivity in broadcast programs. For example, in the case of a broadcast program which provides multiple-choice questions, by transmitting an answer together with video data, on the television receiver side, answer menu buttons are prepared on the computer display, and answer checking can be performed in response to an answering operation using the mouse and cursor keys.
Furthermore, if interactivity is improved, a television receiver in a household, in addition to handling video content, can be expected to make a great advance as an information control station. For example, a television receiver can also become an Internet terminal or an electronic commerce terminal.
In efforts in digital satellite broadcast standardization, as a form (format) of digital broadcast data, use of MHEG (Multimedia and Hypermedia Expert Group) has conventionally been studied. MHEG is one type of markup description language that uses tags which define data attributes, and assumes applications in which multimedia contents are displayed on a television and a viewer extracts desired information in video on demand (VOD) and digital television broadcasts. For example, in a CS digital broadcast (SKYPerfectTV) in Japan, MHEG-5 is adopted.
However, in the MHEG, the definitions of tags are predetermined, and extendibility is lacking. That is, since only tags which are defined uniquely can be used for description, for example, a considerable amount of correction is necessary even to change one function (API (Application Programming Interface)). Also, since MHEG is designed for commercial broadcasts and specifies a method of presentation, it has a relatively low compatibility with general-purpose computers.
Accordingly, in place of MHEG, a specification based on XML (extended Markup Language) is being studied. As is already well known in the industry, similarly to HTML (Hyper Text Markup Language) which is the Internet description language at present, XML is a markup description language which delimits content data using tags in order to specify the attributes thereof. It is also possible for XML to embed a link (that is, to access information (reference) to another resource object) into contents in a manner similar to HTML.
In XML, since the definitions of tags are arbitrary, that is, there is no limitation on the way to describe attributes, a high degree of freedom and high compatibility with computers and the Internet are points which can be mentioned as being more advantageous than in MHEG. Also, planning for XML to become the next generation Internet description language is under way.
As a result of the adoption of XML, the compatibility of broadcast data with respect to computers is further improved. Also, since the compatibility with the Internet is great, it is easy to provide a digital television receiver with the role of an Internet receiving terminal.
The specifications of XML can be broadly classified into xe2x80x9cbasic XMLxe2x80x9d and xe2x80x9cadvanced XMLxe2x80x9d (which is an extended version of the basic XML). The basic XML specifies that the presentation form for expressing transmission contents on a display be described using tags.
In contrast, in the advanced XML, attribute information of transmission contents can be added. A conversion that defines a method (that is, the grammar of tags) for describing attribute information is a standard convention called xe2x80x9cDTD (Document Type Definition)xe2x80x9d. Although DTD is fixed in the basic XML, in the advanced XML, DTD can be defined as desired, and for example, DTD can be defined for each industry. The attribute information referred to herein includes information necessary for each apparatus to understand the meaning of contents and to process them when a connection is made among different apparatuses, such as a television receiver and a computer.
Also, a method for expressing XML contents (that is, a presentation form on a display and a print output form to a printer) is described by a style sheet which is a document which differs from the DTD. For example, by changing the typefaces, the sizes thereof, the colors, etc., in the description order in the style sheet, the same DTD contents can be expressed in a completely different form. The style sheet is transmitted as a file which differs from the DTD. The style sheet for an XML document is specifically called xe2x80x9cXSL (eXtensible Stylesheet Language)xe2x80x9d. XSL has attracted attention as a conversion language for XML documents in addition to its primary function of a style sheet.
As shown in FIG. 17, the distribution of XML contents involves DTD and XSL documents in addition to an XML document. However, the document body is not necessarily limited to an XML document and may be in another markup language format, such as SGML (Standard Generalized Markup Language) and HTML. Also, in the case where a document described by XML is applied to, for example, a television broadcast, and it operates together with other multimedia contents so as to perform the presentation of the contents, it is assumed that the multimedia content is also contained in the document body.
On the receiving side, these received documents are parsed by a syntax analysis program called an xe2x80x9cXML parserxe2x80x9d. The XML parser analyzes an XML document by using a DTD document and outputs a document object. This document object is a structured document in which a tree structure is formed according to the tags in the original XML document.
Then, this document object is converted by a conversion program called an xe2x80x9cXSL processorxe2x80x9d. The XSL processor converts an XSL document into, for example, a script form and converts a document object into an expression form in conformance with the description of an XSL document. For example, a document described in an advanced XML format can be converted into a document of an HTML form which can be browsed by what is commonly called an xe2x80x9cHTML browserxe2x80x9d, or can be converted into a custom document which can be browsed by a custom browser other than HTML.
As stated earlier, even in the case of the same XML content, form of the display on the display screen differs greatly merely by changing the style sheet. That is, the style sheet has a role in providing an added value to the original XML content. In the future, the value of the style sheets will increase further, and it is anticipated that attractive, elaborate style sheets will be produced by professional designers.
However, as style sheets, that is, the XSL documents comes to have added functionality or a great added value, the document size increases. In the case of a complex style sheet, there is a possibility that the data size will be larger than the XML document body. If such a large XSL document is transmitted each time an XML document is transmitted, there will be excessive load on the limited bandwidth. In particular, if a style sheet in a fixed form, such as an electronic program guide or an advertisement, is transmitted each time, the amount of bandwidth used is considerable.
On the other hand, a style sheet having an additional value, such as that produced by a professional designer, is separated from the XML document body, and even the style sheet itself can be a commodity, that is, an object for commercial transaction. Also, since the style sheet itself has a use value as authored works, it is necessary to protect against use without permission and unauthorized use.
Therefore, a technology for effectively managing style sheets and a protection technology capable of preventing use without permission of style sheets are desired.
An object of the present invention is to provide a superior style sheet management technology which is capable of appropriately managing style sheets which define the expression form, etc., of digital data in a computer language format. Digital data in a computer language format is described by, for example, a markup language (for example, XML (eXtensible Markup Language)) in which tags which can be defined arbitrarily are used.
Another object of the present invention is to provide a superior style sheet management technology which is capable of appropriately managing style sheets (for example, XSL (eXtensible Stylesheet Language) data) defining the expression form, etc., of an XML document.
Yet another object of the present invention is to provide a superior style sheet management technology which is capable of appropriately preventing use without permission of style sheets (for example, XSL (eXtensible Stylesheet Language) data) for defining the digital data expression form, etc., such as that described by, for example, an XML format.
The present invention has been achieved in consideration of the above-described objects. In accordance with a first aspect of the present invention, there is provided a data distribution method and apparatus for distributing data described by a computer language, comprising: a step or means for adding a content identifier which is unique to a distribution data content in a computer language format to the data content; a step or means for adding a style identifier which is unique to a style sheet which defines the expression form of the distribution data content to the distribution data content; and a step or means for distributing the distribution data content. The computer language herein refers to a markup language in which tags which can be defined arbitrarily are used, an example thereof being an XML (eXtensible Markup Language) language.
The data distribution method or apparatus in accordance with the first aspect of the present invention may include a step or means for producing a disenabled style using-right key and adding it to the distribution data content. This style using-right key may be produced by concatenating, for example, a content identifier and a style identifier.
The step or means for distributing the distribution data content does not necessarily involve the distribution of a style sheet corresponding to the style identifier added to the distribution data content.
In a second aspect of the present invention, there is provided a data receiving method or apparatus for receiving data described by a computer language, wherein a distribution data content in a computer language format is received in a form in which a unique style identifier is attached to a style sheet which defines the expression form of the distribution data content. The xe2x80x9ccomputer languagexe2x80x9d herein refers to, for example, a markup language in which tags which can be defined arbitrarily are used, an example thereof being an XML (eXtensible Markup Language) language.
In the data receiving method or apparatus in the second aspect of the present invention, a distribution data content to be received may have a disabled style using-right key produced using a style identifier. In this case, the data receiving method or apparatus preferably includes a step or means for enabling the style using-right key in accordance with a purchase procedure.
The data receiving method or apparatus in accordance with the second aspect of the present invention may further comprise: a step or means for performing authentication using an enabled style using-right key; and a step or means for allowing the application of the style sheet in response to the authentication being successful.
In accordance with a third aspect of the present invention, there is provided a data receiving apparatus for distributing data in a computer language format, comprising: a first storage section for storing a data content in a meta-language form within the received data; and a second storage section for storing a style sheet which defines the expression form of the data content independently of the data content. The computer language herein refers to a markup language in which tags which can be defined arbitrarily are used, an example thereof being an XML (eXtensible Markup Language) language.
The second storage section can perform management according to a style identifier possessed uniquely by each style sheet.
According to the receiving system embodying the present invention, style sheets can be stored separately from digital data described by a computer language, and can be managed. As a result, there is no need to individually add a style sheet to each distribution data body and to transmit it, making it possible to reduce the amount of the data transmitted. In particular, in the case where the style sheet comes to have added functionality and is large, the reduction in communication load is enormous. It is also possible to realize an environment in which only the style sheet is reused. The computer language herein refers to, for example, a markup language in which tags which can be defined arbitrarily are used, an example thereof being an XML (eXtensible Markup Language) language.
In addition, according to the receiving system of the present invention, since a style sheet is protected against unauthorized use by attaching key data thereto, it is possible to manage the style sheets as authored works. Furthermore, provision of a means for specifying the other party or for performing authentication also makes limited use of the style sheet possible.
Further objects, features, and advantages of the invention will be apparent from the following detailed description taken in conjunction with the embodiments of the present invention, to be described later, and the accompanying drawings.